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United States Patent |
5,187,021
|
Vydra
,   et al.
|
February 16, 1993
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Coated and whiskered fibers for use in composite materials
Abstract
Diamond and ceramic whiskers 712 are grown on diamond, ceramic, or metal
coated 714 fibers 710 (e.g. carbon, glass, ceramic or metal fibers) and
used in composites 700. The whiskers 712 1) increase fiber-matrix bonding,
2) maintain fiber separation and 3) provide uniform fiber distribution.
The coating 714 1) improves the mechanical properties of the fiber and 2)
protects the fiber 710 from corrosive attack by the matrix material 720. A
catalytic process for growing whiskers 712 allows fiber strength to be
maintained during the whisker growth process. Composite materials made
with whiskered or coated and whiskered fibers are useful whenever
light-weight and high strength materials are required.
Inventors:
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Vydra; Jacob (Worthington, OH);
Altshuler; Anatoly (Lynn, MA)
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Assignee:
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Diamond Fiber Composites, Inc. (Columbus, OH)
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Appl. No.:
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307826 |
Filed:
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February 8, 1989 |
Current U.S. Class: |
428/607; 428/378; 428/380; 428/397; 428/400; 428/614 |
Intern'l Class: |
C22C 001/09; B32B 005/00 |
Field of Search: |
428/614,608,607,375,378,380,381,384,397,400
|
References Cited
U.S. Patent Documents
3252814 | May., 1966 | Russell et al. | 106/57.
|
3580731 | May., 1971 | Milewski et al. | 117/66.
|
3808087 | Apr., 1974 | Milewski et al. | 161/72.
|
4397901 | Aug., 1983 | Warren | 428/375.
|
4402943 | Sep., 1983 | Aisenberg et al. | 427/38.
|
4612233 | Sep., 1986 | Kiergursky et al. | 428/380.
|
4892693 | Jan., 1990 | Perrotta et al. | 164/97.
|
4960654 | Oct., 1990 | Yoshinaka et al. | 428/614.
|
Foreign Patent Documents |
920033 | Jan., 1973 | CA | 156/610.
|
748077 | May., 1977 | CA.
| |
295688 | Nov., 1987 | EP.
| |
325797 | Aug., 1989 | EP | 428/614.
|
Other References
Dergunova et al., "Composites Based on Whiskered Fibers" in Fiber-like
Crystals and Thin Films, Proceedings of the IInd All Union Scientific
Conference, Voronezh 1975 p. 373.
Gunyayev et al., "Effect of Whiskerization of Carbon Fibers on the Physical
and Mechanical Properties of Composites based thereon" in Fiber-like
Crystals and Thin Films. Proceedings of the IInd All Union Scientific
Conference, Voronezh 1975, p. 379.
Towata and Yumada, "Mechanical Properties of Aluminum Alloy Composites with
Hybrid Reinforcements of Continuous Fiber and Whisker or Particulate" in
Composites '86: Recent Advances in Japan and the United States p. 497.
Butuzov et al., "Growth of Diamond Whiskers in a Metal-Carbon System at
High Temperatures and Pressures" in Sov. Phys. Dokl., vol. 20, No. 11, p.
717.
|
Primary Examiner: Zimmerman; John
Attorney, Agent or Firm: Watkins, Dunbar & Pollick
Claims
What is claimed is:
1. A coated and whiskered fiber comprising:
a) a core fiber,
b) a continuous, uninterrupted coating deposited on said core fiber, and
c) whiskers intimately attached to and projecting outwardly from said
coating.
2. The coated and whiskered fiber according to claim 1 wherein said core
fiber is a fiber selected from the group of fibers consisting of
carbonaceous fibers, ceramic fibers, glass fibers and metal fibers.
3. The coated and whiskered fiber according to claim 2 wherein said
carbonaceous fiber is a carbon fiber.
4. The coated and whiskered fiber according to claim 3 with said carbon
fiber is made from polyacrylonitrile.
5. The coated and whiskered fiber according to claim 2 wherein said ceramic
fiber is a silicon carbide fiber.
6. The coated and whiskered fiber according to claim 2 wherein said glass
fiber is an S-type glass fiber.
7. The coated and whiskered fiber according to claim 2 wherein said metal
fiber is a tungsten-based alloy fiber.
8. The coated and whiskered fiber according to claim 1 wherein said coating
is formed from the group of coating materials consisting of metals,
ceramics, and diamond materials.
9. The coated and whiskered fiber according to claim 8 wherein said metal
coating material is nickel.
10. The coated and whiskered fiber according to claim 8 wherein said
ceramic coating material is silicon carbide.
11. The coated and whiskered fiber according to claim 8 wherein said
coating material is diamond.
12. The coated and whiskered fiber according to claim 1 wherein the
material from which said whiskers are formed is diamond or a ceramic
material.
13. The coated and whiskered fiber according to claim 12 wherein said
whisker ceramic material is selected from the group of ceramic materials
consisting of silicon nitride, silicon carbide, titanium carbide and
titanium oxide.
14. The coated and whiskered fiber according to claim 13 wherein said
whisker ceramic material is silicon carbide.
15. The coated and whiskered fiber according to claim 12 wherein said
whisker material is diamond.
16. The coated and whiskered fiber according to claim 15 wherein said
coating is a diamond coating.
17. The coated and whiskered fiber according to claim 16 wherein said core
fiber is a carbon fiber.
18. A composite material reinforced with coated and whiskered fibers
comprising:
a) the diamond coated and diamond whiskered material of claim 16, and
b) a matrix material.
19. A composite material reinforced with coated and whiskered fibers
comprising:
a) fibers having a continuous, uninterrupted coating that completely covers
and surrounds each fiber;
b) whiskers intimately attached to and projecting outwardly from said
coating; and
c) a matrix material.
20. The composite material reinforced with coated and whiskered fibers
according to claim 19 wherein said matrix material is selected from the
group of matrix materials consisting of glasses, metals, polymeric
materials, and ceramic materials.
21. The composite material reinforced with coated and whiskered fibers
according to claim 20 wherein said matrix material is an aluminum or
magnesium alloy.
22. The composite material reinforced with coated and whiskered fibers
according to claim 20 wherein said polymer is a polymer of
4,4'-carbonylbis 1,2-benzenedicarboxylic acid with 4-methyl-1,3-
benzenediamine and 4,4'-methylenebis[benzenamine].
23. The composite material reinforced with coated and whiskered fibers
according to claim 19 wherein said fibers are selected from the group of
fibers consisting of carbonaceous fibers, ceramic fibers, glass fibers,
and metal fibers.
24. The composite material reinforced with coated and whiskered fibers
according to claim 19 wherein said whiskers are ceramic whiskers or
diamond whiskers.
25. The composite material reinforced with coated and whiskered fibers
according to claim 19 wherein said coating is selected from the group of
coatings consisting of metals, ceramics and diamond.
Description
FIELD
This invention relates to coated and whiskered fibers. More particularly,
this invention relates to fibers that have protective coatings and
whiskers and are designed for use in composite materials.
BACKGROUND OF THE INVENTION
Interactions between the fibers and matrix of continuous fiber reinforced
composite materials that occur during manufacture and in use determine the
mechanical properties, fracture behavior, and service characteristics of
these materials. The inherent fiber-matrix compatibility and the composite
manufacturing process must result in a strong bond between the fibers and
the matrix and, at the same time, minimize the dissolution of the fiber in
the matrix and reaction diffusion between the matrix and the fiber
materials. The lack of a strong bond between the fibers and the matrix,
the dissolution of the fibers in the matrix, and reaction diffusion at the
fiber-matrix interface cause bond breaking, delamination, internal stress,
fracture, and other types of failures.
Conventional solutions to these problems include 1) the surface treatment
of fibers with barrier coatings to preserve the fiber and the interface
boundary strength, 2) the development of various combinations of
compatible matrix and fiber materials, and 3) the addition of particulate
additives to more evenly distribute fibers in the matrix throughout the
composite and to serve as an interlocking mechanism between the fibers and
matrix.
In the area of surface treated fibers, U.S. Pat. No. 4,097,624, June 27,
1978 to Schladitz describes a method of coating glass or carbon fibers
with 3 .mu.m-thick Ni layer to minimize the fiber-matrix interaction.
Similarly, the coating of carbon fibers with Mo or Cr layers followed by
application of a SiC barrier coating is described in "Composite
Materials," Baikov Institute for Metallurgy, USSR Academy of Sciences,
Moscow, Nauka Publishing House, 1981, p. 71 and in D. Clark, N. J.
Wadsworth, and W. Watt; "The Surface Treatment of Carbon Fibers for
Increasing the Interlaminar Shear Strength of CFRP" in Carbon Fibers;
Place Mod. Techno. London, 1974, p. 44-51.
Unfortunately barrier coatings using prior art methods and materials do not
result in the simultaneous achievement of good adhesion between the fiber
and the matrix and the prevention of interaction-diffusion at the
interface. Carbide, nitride, or oxide barrier layers with high-temperature
chemical stability hinder the formation of strong physico-chemical bonds
between the matrix and the fiber resulting in separation of fibers from
the matrix and the conglomeration of individual fibers. As a result,
cracks tend to develop at the point of fiber to fiber contact.
A second method to achieve stronger composite materials is by enhancing the
fiber-matrix bond through the improvement of the wettability of the
fibers. This is achieved by coating the fibers or doping the matrix
material. For example, carbon fibers are coated with less than a 1 .mu.m
thick nickel layer to improve their wettability by an aluminum melt;
aluminum is doped with up to 7% silicon and 0.6% magnesium to alter the
adhesion mechanism at the fiber-matrix interface. "Cast Reinforced Metal
Composites," Conference Proceedings, ASM International, 1988 p. 67.
Although this approach enhances the physicochemical bonding between the
fibers and matrix, it, unfortunately, causes dissolution of the fibers and
the formation of intermediate phases and compounds that lessen the
mechanical strength of the composite.
A third approach to obtaining stronger composite materials has been to use
particulates that separate the fibers and interlock fibers and matrix. S.
Towata and S. Yamada, "Composites 86: Recent Advances in Japan and the
Untied States," Ed. Proc. Japan-U.S. CCM-III Tokyo, 1986, pp. 497-503,
describe an aluminum alloy reinforced with continuous carbon or silicon
carbide fibers in which silicon carbide whiskers or other fine particles
are distributed among the continuous fibers. Soviet researchers have grown
SiC whiskers directly on the bare surface of carbon fibers and then have
incorporated the fibers into polymer-matrix composites. "Composite
Materials based on Whiskered Fibers" and published in "Fiber-like Crystals
and Thin Films", Proceedings of the IInd All-Union
Scientific Conference, Voronezh 1975, p. 373. In both of these cases, the
shear strength of the composite material increased; however, because there
is an absence of a barrier coating on the continuous fibers,
disintegration of the fibers caused either by a chemical reaction between
the fibers and the matrix material or by the whiskering process or both
takes place resulting in a significant loss of composite material
strength. When carbon fibers were whiskered at 3 wt. % to obtain optimal
composite shear strength, the carbon-fiber strength decreased by a factor
of two.
SUMMARY OF THE INVENTION
The above-described problems associated with fiber reinforced composites
are solved by the present invention of a catalytically prepared whiskered
fiber or a coated and whiskered fiber. The core fiber may be any suitable
continuous fiber such as, but not limited to, carbonaceous, ceramic, glass
and metal (including metal-alloy) fiber. The fiber coating (film) is made
from any suitable material such as, but not limited to, metal (including
metal-alloy), ceramic, diamond and diamond-like materials. The coating is
applied to the fiber prior to whisker growth or, alternatively, to both
the fiber and whiskers after the whiskers have been grown on the fiber.
The whiskers are intimately attached to the fiber or, alternatively, are
intimately attached to the coating of a coated fiber after a suitable
coating film has been applied. The whiskers are distributed randomly over
the radial surface of the fiber and project outwardly therefrom. The
whiskers are grown from any suitable material such as diamond or ceramic
materials, e.g., silicon nitride, silicon carbide, titanium carbide, or
titanium oxide.
The projecting whiskers on a fiber offer the following advantages over a
conventional composite fiber:
a) they strongly bind fibers with the matrix due to the micromechanical
interaction through the whiskers thereby preventing delamination of the
composite material and greatly increasing the composite shear strength;
the mechanical properties of diamond and ceramic whiskers are the highest
among known materials;
b) they maintain a separation of the fibers from each other thereby
preventing their conglomeration and formation of nonimpregnated groups of
filaments or the initiation of local stress sites; and
c) they provide a favorable fiber distribution in the matrix and a
resulting decrease in thermally and mechanically induced internal
stresses.
A coating applied to the fiber either prior to or after the whiskering
process provides the following additional advantages:
a) it improves the mechanical properties of the fibers by healing surface
defects and perfecting the surface structure; and
b) it ensures substantial protection of the fibers from the matrix
material.
A coating applied prior to the whiskering process serves to further protect
the fiber from the heat and chemical environment of the whiskering process
and thereby serves to maintain the strength of the fiber.
By using diamond coatings and whiskers on reinforcing continuous fibers,
the theoretical limits of strength and heat resistance of composite
materials become attainable. The strength of metal matrix composites, for
example, can be increased by a factor of 1.5-2, reaching, in some cases,
3,700-4,000 MPa. Diffusion processes through a diamond coating are minimal
up to about 1300.degree. C.; volume graphitization of diamond under
atmospheric pressure does not begin until 1500.degree. C.
Providing the fiber with a protective coating improves the service
characteristics of the composite material by protecting the fiber from the
matrix material. Although a protective coating can be applied after the
whiskers are grown on the fiber, in many instances it is desirable to
apply such a protective coating prior to the whisker growth process. For
example, an initial protective coating is desirable to protect the fiber
from the harsh environment and temperatures of the whiskering process.
Also an initial fiber coating can improve the mechanical properties of the
fiber by healing surface defects and perfecting the surface structure
prior to the whiskering process.
A protective metal, ceramic, diamond or diamond-like film or coating is
formed on the fibers by using conventional in vacuo wetting processes as
well as electrochemical and vacuum spraying techniques. For example,
silicon carbide and titanium carbide coatings are formed on
polyacrylonitrile (PAN) based carbon fibers by in-vacuo wetting of the
fiber in metal melts of aluminum, silicon and copper or aluminum, titanium
and copper followed by annealing of the metal-coated fibers in vacuum or
an inert atmosphere. Diamond-coated fibers are made by depositing a
diamond film on the fiber using a high energy plasma source that creates
ions and electrons and contains a suitable hydrocarbon gas such as methane
thereby affording carbon atoms and ions. Carbon atoms and ions can also be
obtained from carbon electrodes that are electrically heated so as to
sputter carbon ions uniformly about and against the fiber surface.
Alternatively the fibers can be coated with a diamond-like coating by
first depositing amorphous carbon film on the surface of the fiber using a
low-energy hydrocarbon containing ion beam and then transforming the
amorphous carbon into diamond-like carbon by exposing the amorphous carbon
surface to a high-energy ion beam that simultaneously converts the
amorphous carbon to diamond-like carbon while removing lesser bound carbon
atoms from the deposited film.
Cleaning of the surface of the core fiber prior to deposition of the
coating material enhances the bond between the fiber and the coating
material. For example, a barrage of high energy or energetic plasma
created ions and electrons against a fiber removes surface contaminants
and diminishes microscopic surface defects. The freshly exposed, i.e., ion
milled surface enhances deposition of a coating material by increasing the
strength of the bond between the fiber surface and the coating.
A whiskered fiber increases matrix fiber binding as a result of whisker
interaction while at the same time maintaining fiber separation and
improving fiber distribution in the matrix. Whiskers are grown on either a
bare or coated fiber by first applying a uniform dispersion of "whisker
growth" particles to the fiber surface and then drying the fiber to remove
any solvent. The whisker growth particles serve as a site for initiating
and promoting whisker growth. Typically the whisker growth particles are
rare earth or transition metals or transition metal compounds such as
lanthanum or iron or compounds such as iron trichloride, iron
pentacarbonyl or nickel tetracarbonyl that decompose to give finely
divided nascent metal particles. The particle treated fiber is then fed
into a vacuum chamber containing a hot gaseous mixture of whisker forming
material. As the hot gaseous mixture strikes the relatively cool fiber, an
extreme super saturation of the mixture takes place at the particle
nucleation site with subsequent whisker growth via a vapor-liquid-solid
mechanism at a rate of several microns per minute.
The presence of a volatile transition metal compound such as ferrocene
Fe(C.sub.5 H.sub.5).sub.2, iron pentacarbonyl Fe(CO).sub.5, nickel
tetracarbonyl Ni(CO).sub.4 or dicobolt octacarbonyl Co.sub.2 (CO).sub.8
also acts as a catalyst to significantly reduce the temperature at which
the reactant substances (materials) combine to give the whisker forming
material. For example, the formation of silicon carbide takes place at
temperatures above 1500.degree. C. However, by using a catalyst, the
temperature can be lowered to about 1000.degree. C. and preferably to
approximately 900.degree. C. thereby eliminating the fiber weakening
effects caused by higher temperatures. As a result of the lower
temperatures afforded through the use of a catalyst, it is possible to
grow whiskers directly on a fiber without loss of the fiber strength
previously encountered.
For example, to prepare silicon carbide (SiC) whiskers, the reaction of the
substances silicon tetrachloride and methane in the presence of hydrogen
and with a ferrocene catalyst occurs to produce silicon carbide according
to the following reaction scheme:
##STR1##
SiC whiskers begin to form and continue to grow at the particle nucleation
site previously applied to the fiber.
For the preparation of diamond whiskers, the substance carbon tetrachloride
is reacted with the substance methane in the presence of hydrogen with
ferrocene as the catalyst according to the following scheme:
##STR2##
To prepare silicon nitride, the substances silicon tetrachloride,
nitrogen, and hydrogen are reacted according to the following reaction
scheme using ferrocene as the reaction catalyst:
##STR3##
Coated and whiskered fibers are particularly useful as a reinforcing
material for composite materials. For example, whiskered or coated and
whiskered fibers can be shaped into a preform with the whiskers serving to
maintain an even distribution of the fibers in the preform. The preform is
then set into a die cavity into which a molten matrix material is poured.
The preform and molten matrix material are then squeezed to form a
composite reinforced with whiskered fibers or coated and whiskered fibers.
In such a process, the matrix material is typically a molten metal such as
magnesium or aluminum alloys.
In another method of making composite materials, alternate layers of metal
foil, e.g., aluminum foil, and whiskered fibers or coated and whiskered
fibers are prepared. These alternate layers of fibers and metal foil are
then rolled to form a composite sheet. In the sheet rolling technique, the
whiskered or coated and whiskered fibers can be arranged in a
criss-crossing fashion to further improve the strength of the resulting
composite material.
It is an object of this invention to provide a whiskered fiber or a coated
and whiskered fiber that interlocks with other similar fibers in a matrix
material to provide a composite material of superior strength and crack
and stress resistance. Composite materials reinforced with such whiskered
or whiskered and coated fibers are useful as lightweight armor, automobile
parts, ship and space vehicle components, and for other purposes requiring
light-weight and very high-strength materials.
Other objects and features of the invention will be apparent and understood
from the detailed description of the invention and the accompanying
drawings which follow. The foregoing and other advantages of the invention
will become apparent from the following disclosure in which the preferred
embodiment of the invention is described in detail and illustrated in the
accompanying drawings. It is contemplated that variations and procedures,
structural features and arrangements of materials may appear to the person
skilled in the art without departing from the scope or sacrificing any of
the advantages of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal cross-sectional view of a whiskered fiber; FIG. 2
is a longitudinal cross-sectional view of a whiskered and coated fiber;
FIG. 3 is a longitudinal cross-sectional view of a coated and whiskered
fiber;
FIG. 4 is a lateral cross-sectional view of a coated and whiskered fiber;
FIG. 5 is a sectional view of an apparatus for applying a continuous
coating on the surface of a fiber;
FIG. 6 is a sectional view of an apparatus for applying and drying an
atomized catalyst on the surface of a fiber;
FIG. 7 is a sectional view of an apparatus for growing whiskers on a fiber;
and
FIG. 8 is a cross-sectional view of a composite formed from coated and
whiskered fibers showing the interlocking action of the whiskered fiber.
In describing the preferred embodiment of the invention which is
illustrated in the drawings, specific terminology is resorted to for the
sake of clarity. However, it is not intended that the invention be limited
to the specific terms so selected and it is to be understood that each
specific term includes all technical equivalence which operate in a
similar manner to accomplish a similar purpose.
Although a preferred embodiment of the invention has been herein described,
it will be understood that various changes and modifications in the
illustrated and described structure can be effective without departure
from the basic principle that underlay the invention. Changes and
modifications of this type are therefore deemed to be circumscribed by the
spirit and scope of the invention, except as the same may be necessarily
modified by the appended claims or reasonable equivalence thereof.
DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE FOR CARRYING OUT THE
PREFERRED EMBODIMENT
Referring now to the drawings wherein the representations are for the
purpose of illustrating the preferred embodiments of the invention only
and are not for the purpose of limiting the same, FIGS. 1-4, show a
whiskered fiber generally denoted by the number 5 (FIG. 1), a whiskered
and then coated fiber denoted by the number 7 (FIG. 2), and a coated and
then whiskered fiber denoted by the number 10 (FIGS. 3-4). The fiber,
coating material, and whisker material are denoted by the numbers, 12, 14,
and 16, respectively. Generally a fiber that is whiskered only 5 is used
when fiber/composite matrix material weakening interactions and reactions
are negligible but fiber distribution and separation are of importance. A
fiber that is first whiskered and then coated 7 is used when weakening
interactions and reactions among the composite matrix material, the fiber,
and the whisker material are significant. A fiber that is first coated and
then whiskered 10 is used when weakening interactions and reactions
between the fiber and composite matrix material are of primary
consideration while composite matrix material and whisker material
interactions and reactions are minimal. Also it may be important to coat
the fiber first so as to protect the fiber from the high temperature and
chemical environment of the whiskering process.
The core fiber 12 must be of a suitable material of sufficient strength and
durability so as to be able to withstand the whiskering or coating and
whiskering process. A wide range of such materials are known. For example,
carbonaceous fibers include carbon fibers such as PAN fibers prepared from
polyacrylonitrile, graphite fibers, and diamond fibers that are prepared
by sintering diamond whiskers. Ceramic fibers include a wide variety of
carbides, borides, nitrides, and oxides of a wide variety of elements
including transition metal elements such as titanium and zirconium, rare
earth elements such as hafnium, and main group elements such as silicon
and boron. Glass fibers include S-2 type fibers which are high strength
aluminum-magnesium-silicon glass fibers. Metal fibers (including metal
alloy fibers) are illustrated by tungsten and tungsten-based alloy fibers.
As shown in FIGS. 2, 3 and 4, a coating or film 14 completely surrounds
and covers fiber 12, i.e., a continuous, uninterrupted coating. This
coating or film 14 can be formed from metal (including metal alloys),
ceramic, and diamond and diamond-like materials.
The terms diamond-like and diamond are used interchangeably with regard to
the properties of the crystalline carbonaceous material coating or film 14
found on fiber 12 (FIGS. 3 and 4) or on the fiber 12 and whiskers 14. The
term "diamond-like" conventionally is used to distinguish the structure of
the crystalline carbon film on the fiber 12 or whiskers 14 from the
structure of non-film diamond crystals. However, it is noted that both
diamond-like and diamond crystals are both crystalline materials having
the same properties, e.g., (1) a similar index of refraction (2) high
electrical resistivity (3) transparency in the visible light range, (4)
high dielectric constant, (5) the ability to abrade glass, and (6) high
resistivity to hydrofluoric acid etching. For the purposes of this
description, the term "diamond" includes the term "diamond-like."
As will be described in more detail later on, the diamond-like coating is
applied to the fiber by vaporizing atoms of carbon on the fiber 12 or by
sputtering carbon atoms from electrodes onto the surface of the fiber and
then transforming the graphite structure of the coating into a diamond
structure. Similar techniques can be used to apply ceramic and metal
coatings.
The whiskers 16 are single crystal fibers that have mechanical strengths
approaching interatomic bonding forces. Typically the whiskers 16 are
diamond, silicon nitride, silicon carbide, titanium oxide, or other high
strength ceramic-type material. Whiskers 16 are grown on the surface of
the fiber 12 or on the coating 14 by depositing particles on the fiber 12
or fiber coating 14 that serve to initiate and support whisker growth.
Preferably these particles are atomized metal particles or a compound
capable of being readily converted to metal particles, e.g., iron
pentacarbonyl. The whiskers are typically grown at the particle
(nucleation) sites, which are typically molten atomized metal particles,
by a vapor-liquid-solid mechanism in which the gaseous components of the
whisker material condense and react on the molten metal particle to form a
supersaturated solution from which the solid whisker grows at a rapid
rate. For the purposes of this invention, the gaseous components of the
whisker material as well as the whisker materials themselves are referred
to as whisker forming material.
In accordance with one aspect of this invention, the core fiber 12 is
coated with a diamond film by depositing carbon ions onto the fiber using
plasma ion deposition techniques and apparatus as are found in U.S. Pat.
No. 4,402,993 and U.S. Pat. No. 4,530,750 all of which said patents are
incorporated herein by reference. As shown in FIG. 5, the fiber 12 to be
coated is fed from a spool 20 over roller 22 into the coating apparatus
30. The fiber 12 enters the coating apparatus 30 through an insert orifice
32 in endplate 34. Plates similar to plate 34 with a centering insert
orifice 32 are used throughout the apparatus to provide various barriers
and to define chambers and zones at various axial positions within the
apparatus 30. The orifice 32 is of a snap-in type so that it can be
readily exchanged for other orifices with differing interior bores to
accommodate different diameter fibers or to give additional clearance as a
result of coatings deposited on the fiber. Typically the interior surfaces
of these orifices are coated with Teflon, hardened chrome, or other
hardened, heat resistance friction-reducing surface materials. Generally,
the orifices have a diameter that is only slightly larger than the
diameter of the fiber so as to maintain centering of the fiber and at the
same time allowing for the creation of air locks, vacuum chambers, and
other operational environments within apparatus 30.
After entering through orifice 32, the fiber passes into airlock 40 which
consists of a tube 36 which is axially centered about fiber 12 by means of
plates 38 and 41. Gas inlet ports 42 are tangentially attached to tube 36
so that an inert gas such as argon may be fed through tubes 42 into tube
36 and thereby create a swirling vortex that surrounds the incoming fiber
12. This swirling inert gas vortex tends to dislodge and remove
contaminants such as lint and loose material on fiber 12.
The fiber 12 then enters into vacuum chamber 50 through orifice 44 in plate
46. The vacuum chamber 50 is composed of several stages, 53, 55 and 57,
each of increasing vacuum. Each stage of the vacuum section is evacuated
by connection 58 to a vacuum pump (not shown). A sufficient number of
vacuum stages is provided to result in a vacuum in the final stage of
approximately 1.times.10.sup.-6 atmospheres.
After passing through the vacuum section 50, the fiber 12 enters chamber 54
through orifice 52 in plate 48. Chamber 54 is essentially a plasma milling
chamber in which a plasma of ions from plasma source 56 activates argon
ions from an argon source 58 which are injected into the milling chamber
54 through nozzle 60. Coils 62 and 64 create an axially extending magnetic
field which forces the plasma to move upwards in a direction opposite to
the downward movement of fiber 12. The vigorous attack of the ions and
electrons within the plasma moving through coils 62 and 64 creates a
milling action on the outer cylindrical surface of fiber 12 thereby
producing a more perfectly cylindrical outer surface on fiber 12 polishing
out minor surface imperfections including microscopic cracks, hills and
valleys. The electrical coils 62 and 64 are energized by a negative
voltage at lead 65 and a positive voltage at lead 66.
After milling is complete in zone 54, fiber 12 moves through orifice 70 in
plate 72 into the diamond-coating chamber 74. In chamber 74, carbon
electrodes 76 are heated through leads 78 and 80 to glowing so as to emit
ions. The electrodes 76 are spaced uniformly about and against the
downwardly moving surface of fiber 12. The emitted or sputtered carbon
ions bombard, hit and attach to the downwardly moving fiber 12 to provide
a diamond-like carbon coating on fiber 12. In addition, a plasma from
plasma source 82 is mixed with argon from argon source 58 and enters
coating chamber 74 through nozzle 84. The plasma contains elemental carbon
which further enhances the deposition of the diamond-like coating on the
surface of fiber 12. A suitable hydrocarbon gas, such as methane, is used
for creating elemental carbon propelled in plasma ion form against the
surface of the downwardly moving fiber 12. The argon from argon source 58
may be used to fortify the plasma forming operation and as an auxiliary
carrier to introduce deposition coating material into the plasma at a
greater rate.
In chamber 74, it is possible to provide carbon atoms in a substantially
vapor or gaseous form or as a component of gaseous additive hydrocarbon
material for subsequent decomposition into the appropriate ion by means of
the plasma energy from the appropriate plasma source 82. Such action is
referred to as plasma pyrolysis. Use of a hydrocarbon gas aids in the
desired deposition of a special type of carbon crystal film on the
downwardly moving fiber 12 since the ions of the plasma thereby being
formed are directed against the moving fiber 12 are carbon ions and
hydrogen ions. The hydrogen ions colliding or bombarding the downwardly
moving fiber or filament 12 assist in removing residual oxygen ions that
may possibly remain on the outer periphery of downwardly moving fiber 12.
Typically the deposition of carbon ions onto the downwardly moving fiber
12 in vacuum zone 74 provides a rate of thickness of about 10-20 angstroms
per second.
The diamond-coated fiber 12 then passes through orifice 86 and into a
vacuum chamber 200 similar to vacuum chamber 50 and consisting of vacuum
stages 202, 204, and 205 and connections 208 to a vacuum pump (not shown).
Fiber 12 then proceeds into airlock 220 similar to airlock 40 and
consisting of a tube 222 and inert gas inlet ports 224. The coated fiber
12 is withdrawn from the apparatus through orifice 93 in end plate 95 over
roller 94 and onto spool 92.
Although the formation of a diamond film 14 on fiber 12 has been
illustrated, it is within the scope of this invention to coat the fiber
with other materials such as ceramics, preferably silicon carbide or
silicon nitride, or metals (including metal alloys) such as nickel,
chromium or titanium and their alloys. A variety of techniques are known
for coating fibers with ceramic materials and metals of which some
illustrative examples are described in U.S. Pat. No. 4,530,750, U.S. Pat.
No. 4,402,993 and D. Clark, N. J. Wadsworth, and W. Watt; "The Surface
Treatment of Carbon Fibers for Increasing the Interlaminar Shear Strength
of CFRP" in Carbon Fibers; Place Mod. Technol., London, 1974, p. 44-51.
When the fiber to be coated with a diamond-like film is sensitive to the
higher temperatures of the plasma deposition process described above, it
is preferable to use the low temperature ion beam technique in which the
film is deposited on the fiber using low-energy ion beams followed by
exposure of the film to a higher energy ion beam which increases the
mobility of the condensing atoms and serves to remove lesser bound atoms.
Such a process is more fully described in U.S. Pat. No. 4,490,229 to
Mirtich et al., all of which said patent is herein incorporated by
reference.
As noted previously, the preferable coating material will depend in many
instances on the selected use of the coated and whiskered fiber. Also as
noted, it is possible to omit the coating material completely and use only
the whiskered fiber. In such cases, the coating process as depicted in
FIG. 5, or as otherwise practiced, may be omitted. However, in any event
it is often desirable to clean the fiber 16 prior to forming a whisker
thereon in order to achieve a stronger bond between the fiber 12 and
whisker 16 or between the fiber 12 and coating 14. In such instances, it
is preferable to use a cleaning process such as the plasma milling process
illustrated in FIG. 5 and described above.
It is also to be understood that a diamond, ceramic, or metal coating may
be applied after a fiber has been whiskered. In such instances, the
coating process described above and depicted in FIG. 5 would follow the
whiskering process described below rather than proceed it. For the
purposes of this invention, a coated and whiskered fiber is considered to
the equivalent to a whiskered and coated fiber and it is to be understood
that one form may be substituted for the other form without departing from
the scope of this invention.
For the sake of clarity, the following whiskering process is described for
growing whiskers on an uncoated fiber. However it is to be understood that
the same process could also be used to grow whiskers 16 on a coated fiber
and that the choice as to whether to apply whiskers directly to the
uncoated fiber or to the coated fiber will depend on the nature of the
application and the physical characteristics of the fiber 12, the whisker
16, and the coating 14.
In the initial stage of the whisker forming operation illustrated in FIGS.
6, the fiber 12 is withdrawn from spool 92 over roller 94 and into
nucleation site forming apparatus 100. Apparatus 100 consists essentially
of two separate chambers, (1) a chamber 98 where atomized metal particles
or metal compounds capable of forming metal particles are applied to fiber
12 and (2) a drying chamber 102 where the carrier for the metal particles
or metal particle forming compound are removed, typically by drying.
As fiber 12 moves through orifice 101 into chamber 98, it is sprayed with a
carrier containing atomized metal particles or a compound capable of
forming metal particles such as transition metal compounds, e.g., iron
pentacarbonyl, dicobalt octacarbonyl, and iron trichloride, and where the
molten form of the resulting metal is conducive to the formation of
whiskers on the fiber 12. Although a carrier, i.e., a solvent preferably
is used to deposit the particles on the fiber, it is to be understood that
other non-solvent techniques such as electrostatic methods may by used and
are considered to be equivalent for the purposes of this invention.
For growing silicon carbide whiskers, a saturated aqueous solution of iron
trichloride is sprayed (atomized) onto the fiber 12 in chamber 98 so as to
produce a fine mist which is directed to all sides of the fiber 12. Excess
iron trichloride solution is returned to the main iron trichloride
solution supply 104 by means of outlet port 106 and return line 108. The
droplets of iron trichloride are evenly distributed around the fiber 12 so
as to give a predefined and controllable surface concentration that will
produce nucleation sites of about 0.5 to 1.5 whiskers per 5 .mu.m of
reduced fiber length.
The diamond fiber 12 which is now coated with droplets of iron trichloride
solution 104, then passes through orifice 110 into drying chamber 102
where it is dried by electrically heated coil 112 at a temperature of
about 600.degree. C. The iron trichloride atomizing, spraying and drying
operations are carried out under atmospheric conditions. After drying, the
fiber 12, covered with solid iron trichloride, exits chamber 104 through
orifice 117 in endplate 118 over pinch rollers 115 and is wound onto spool
116 for further processing.
As noted, a variety of metal producing compounds or metals themselves may
be applied to the fiber. The various compounds that are used require
different application conditions that are known by those skilled in the
art. For example, iron pentacarbonyl undergoes pyrophoric decomposition in
the presence of oxygen and thus iron pentacarbonyl must be applied and
dried in an inert atmosphere such as nitrogen. It is also to be understood
that if a metal compound is used, it must be converted to the metal prior
to whisker growth. Such conversion can be carried out in chamber 102. When
conversion to the metal is carried out in chamber 102, it is desireable to
attach the apparatus shown in FIG. 7 to the apparatus of FIG. 6 so that
the fiber 12 is drawn in the whisker forming apparatus directly from the
apparatus of FIG. 6 without the need for winding onto and off of spools
and thereby avoiding atmospheric contact.
In the whisker growing apparatus 300 illustrated in FIG. 7, fiber 12,
having particles for carrying out whisker growth thereon, is fed from
spool 116 through an airlock 320 and a vacuum chamber facility 350 similar
to airlock 40 and vacuum chamber 50 shown in FIG. 5 and described above.
Airlock 320 consists of a tube 322, gas inlet ports 324, endplate 326 with
orifice 328 and centering plates 330 and 332. Vacuum chamber 350 consists
of stages 352, 354, and 356 that are connected to a vacuum pump (not
shown) by connections 358. The fiber 12 then enters reaction section 400
consisting of three or more reaction zones 410, 420 and 430 separated by
cooling zones 440 and 450. The reaction zones are equipped with electrical
heaters 412, 422 and 432 to heat the metal particles deposited on fiber 12
to the molten state and to maintain the reaction temperature of the
reactants that yield the whisker forming materials. In instances where a
metal compound such as iron trichloride or iron pentacarbonyl has been
applied and not transformed to the metallic state, such a metal forming
process is also carried out in reaction zone 410.
The gaseous whisker forming material is provided at the nucleation site,
i.e., the location of the molten metal droplet on the fiber, in each of
the reaction zones 410, 420 and 430. Thus for growing silicon carbide
whiskers, silicon and carbon species are provided at the nucleation site;
for diamond whiskers, a carbon species is provided; and for silicon
nitride whiskers, silicon and nitrogen species are provided at the
nucleation site. The reactant species react at the site of the molten
metal droplet to form the desired whisker by a vapor-liquid-solid (VLS)
mechanism. The VLS process is known in the art as exemplified by J. V.
Milewski, F. D. Gac, J. J. Petrovic, and S. R. Skaggs; "Growth of the
beta-silicon carbide whiskers by the VLS process" Journal of Material
Science 20(1985) 1160-66.
As shown in FIG. 7, nitrogen 452, hydrogen 454, methane 456, a reactant
458, and a reaction catalyst 460 are mixed in the appropriate proportions
by means of mixing and flow valves 464 and delivered to the reaction
chambers 410, 420, and 430 by means of delivery tubes 480. For example,
for the production of silicon carbide whiskers; nitrogen 452, hydrogen
454, methane 456, a reactant gas 458 such as silicon tetrachloride and a
reaction catalyst 460 such as ferrocene are suitably mixed by using
stopcock and flow control valves 464 to give a mixture of H.sub.2 --82.4,
N.sub.2 --8.4 and CH.sub.4 --8.7 mole %. The mole ratio of H.sub.2 to
SiCl.sub.4 is 1:4 and the average weight ratio of Fe from the ferrocene to
SiC from the reaction mixture is 1:100. The average weight ratio of Si to
C is 1:2.28. The mixture passes through heater 510 to increase the
temperature of the reactants to approximately 500.degree. C. to
1400.degree. C. The reaction mixture is then fed into reaction chambers
410, 420 and 430 which are heated by heating coils 412, 422 and 432 to
approximately 500.degree. C. to 1400.degree. C. and preferably below
1000.degree. C., especially when the whiskers are grown on an uncoated
fiber. As the reaction mixture strikes the relatively cool surface the
particle deposited on fiber 12, supersaturation occurs and reaction
products condense according to a vapor-liquid-solid mechanism which
results in whisker growth of several microns per minute. Whisker growth is
further enhanced by passing the fiber through cooling zones 440 and 450
where the relative coolness of the nucleation particle is maintained.
Growth of whiskers of various types of materials are well known and
described in Canadian Patent 948 077 Maine et al, May 28, 1974 (silicon
carbide whiskers); "Preparation of Diamond Whiskers" in Superhard
Materials: Synthesis, Properties, and Application," Institute for
Superhard Materials, Ukrainian Academy of Science, Proceedings of
International Symposium, Kiev, Naukova Durka, 1983, p. 45 (diamond
whiskers); and V. M. Krivoruchko, "Preparation of Refractory Compounds
from the Gas Phase," Moscow, Atomizdat, 1976, p. 7 (silicon nitride
whiskers). The following reaction schemes are typical of the formation of
silicon carbide, diamond, and silicon nitride whiskers:
##STR4##
The whiskered fiber 12 exits the high temperature reaction chamber 430
through orifice 260 into the vacuum seal 500 similar to vacuum chamber 50
(FIG. 5 described above) and consisting of vacuum stages 510, 520, and 530
that are connected to a vacuum pump (not shown) by connectors 564 and
inert atmosphere airlock 560 similar to airlock 40 (FIG. 5 described
above) and consisting of tube 563 and inert gas inlet ports 564 after
which it is withdrawn through orifice 580 in endplate 582 by pinch rollers
590 and wound onto spool 600.
The whiskered or coated and whiskered fibers are especially useful for
forming composite materials as illustrated in FIG. 8. As shown in FIG. 8,
such composite materials 700 consist of whiskered or coated and whiskered
fiber 710 surrounded by matrix material 720. The whiskers 712 of the
fibers 710 serve several purposes. They maintain each of the fibers in a
fixed position with each of the other fibers so as to provide space there
between which allows for the matrix material 720 to completely engulf and
cover the whiskered fiber 710. The fibers are strongly bound to the matrix
due to the micromechanical interaction of the whiskers with the matrix
which prevents delamination of the composite material and greatly increase
the composite shear strength because of the high strength and Young's
modulus of the whiskers. The whiskers 712 maintain a uniform separation of
the fibers from each other thereby preventing fiber conglomeration and
formation of nonimpregnated groups of fibers which can cause and create
local stress sights. Proper distribution of fibers in the matrix results
in a decrease in thermally and mechanically induced internal stresses.
Finally, when a coating 714 such as a diamond coating that is chemically
inert is used, the disintegration or failure of the fibers caused by a
chemical reaction between the fibers and the matrix material is avoided.
Several techniques are available for the production of composite materials
reinforced with whiskered or coated and whiskered fibers. For example, the
whiskered or coated and whiskered fibers can be integrated into a
composite using a squeeze casting technique. The squeeze casting process
typically involves shaping the whiskered or coated and whiskered fibers
into a preform, that is, layers of strands of the whiskered fiber arranged
parallel to each other and in the general shape of the item to be cast.
Typically, the volume of the whiskered fibers occupies about 10 to 40
volume % of the item to be cast. Once the fibers have been arranged into
the preform, they are placed into a die cavity. A molten matrix material
520, such as molten aluminum or magnesium alloy, is then poured into the
cavity and the preform and molten metal are subjected to the pressure of a
press, so as to squeeze the molten metal in and between the spaces formed
by the whiskers 512 of the fibers 510.
In another technique for forming composite materials, alternate layers of
the matrix material, e.g., aluminum alloy foil, and whiskered fibers are
assembled. The alternate layers of the matrix material and the whiskered
fibers are then heated and rolled (pressure shaped) so as to form a
composite sheet or article. The whiskered fibers can be arranged in
patterns in which the fibers are not all parallel to each other, that is,
in each successive layer, the whiskered fibers can be arranged so that
each layer of fiber is arranged in a different direction from that of the
layer of fibers immediately above or below it, i.e. in a criss-crossing
fashion.
As shown in the following table, a wide variety of fiber and matrix
materials can be chosen to provide a large number of composite materials
for wide and differing applications.
TABLE I
______________________________________
Composite Materials with Reinforcing Fibers having a
Silicon Carbide Coating and Silicon Carbide Whiskers.
MATRIX FIBER
FIBER MATERIAL VOLUME % USE
______________________________________
Thornel 100
Al Alloy 30-45 Structural
Al-94%; material for
Mn-1%; aircraft and
Cu-5% automobile
industry;
lightweight
armor
Thornel 100
Ni Alloy: 40-55 Sheets and
Ni-53.7%; nozzle parts
Co-20.0%; for jet engines
Cr-10.0%;
Mo-5.0%;
Al-5.0%;
Ti-3.7%;
Mn-0.3%;
Si-0.3%;
Fe-1.8%;
C-0.2%;
B-0.02%;
Thornel 100
Polyimide 45-60 Structural
2080 material for
aircraft
industry;
lightweight
armor
Silicon Carbide
Al Alloy: 45-60 Structural
Al-94%; material for
Mn-1%; aircraft
Cu-55 industry
Silicon Carbide
Ni Alloy: 25-50 Blades and vanes
Ni-53.7% of gas turbine
Co-20.0%; engines
Cr-10.0%
Mo-5.0%;
Al-5.0%;
Ti-3.7%;
Mn-0.3%;
Si-0.3%;
Fe-1.8%;
C-0.2%;
B-0.02%;
Silicon Carbide
Ti Alloy: 25-50 Structural
Ti-90%; material for
Al-6%; space industry
V-4%;
S-Glass Al-Alloy: 30-45 Structural
Al-94%; material for
Mn-1%; aircraft and
Cu-5%; automobile
industry;
lightweight
armor
S-Glass Ni-Alloy: 45-55 Blades and vanes
Ni-53.7%; of gas turbine
Co-20.0%; engines
Cr-10.0%;
Mo-5.0%;
Al-5.0%;
Ti-3.7%;
Mn-0.3%;
Si-0.3%;
Fe-1.8%;
C-0.2%;
B-0.02%;
S-Glass Polyamide 45-60 Structural
2080 material for
Aircraft
Industry;
lightweight
armor
W-Re Wire Ni Alloy: 25-50 Combustion
W-80%; Ni-53.7%; chambers and
Re-20% Co-20.0%; blades of gas
Cr-10.0%; turbine engines
Mo-5.0%;
Al-5.0%;
Ti-3.7%;
Mn-0.3%;
Si-0.3%;
Fe-1.8%;
C-0.2%;
B-0.02%;
______________________________________
Thornel 100 (carbon fiber) is a trademark of the Union Carbide
Corporation.
Polyamide 2080 is a polymer of 4,4carbonyl bis 1,2benzenedicarboxylic
acid, with a 4methyl-1,3-benzenediamine and 4,4methylenebis [benzenamine]
It may be possible that changes in the configurations to other than those
shown could be used but that which is shown is preferred and typical.
Without departing from the spirit of this invention, various means of
arranging and forming the various fibers and matrix materials into a
fiber-reinforced composite may be used.
It is therefore understood that although the present invention has been
specifically disclosed with preferred embodiments and examples,
modifications to the design concerning size, shape and materials may be
apparent to those skilled in the art, and such modifications and
variations are considered to be within the scope of the invention and the
appended claims.
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